Cerium(IV)-promoted ethylation of Schiff bases by triethylaluminum

Schiff bases Ar¹CH=NAr² that are refractory towards Et₃Al are activated at room temperature by cerium(IV) compounds. The ethylation takes place selectively at the methine moiety of the imine. The process is strongly influenced by steric hindrance and depends on the electronic nature of the substrate: electron-donating substituents promote the reaction while electron-withdrawing groups cause it to slow down. Application of cerium(IV) ammonium nitrate as promoter gives the best results. In the absence of excess Et₃Al it causes, however, transformation of the Schiff base to the corresponding aldehydes and amines.